This high-density retirement complex in Ellerslie, Auckland, consists of villas, townhouses, apartment buildings (up to seven storeys) and a care facility, plus associated structures including basement carparks.
The 3.9ha brownfield site was previously used as a quarry and a zoo. Basalt lava up to 20m deep underlay the site with a variable surface cover of uncontrolled fill, lava caves and scoriaceous pockets – all complicating the founding requirements.
For pre-purchase due diligence, Riley carried out environmental and geotechnical investigations, and civil assessment and design.
After purchase, our work involved:
further geotechnical investigation
resource consenting and building consent applications
contract management and construction supervision.
Key engineering challenges included:
a major retaining wall structure 250m long and up to 5.7m high. We undertook geotechnical design aspects and construction supervision
design and construction observations for a 2,850m2 pond needing dual functions – landscape amenity, and flood and stormwater detention
geotechnical design of building foundations and ground improvement measures to mitigate the effects of adverse ground conditions
public wastewater and water supply upgrades to increase capacity
rock removal to form basement levels, including explosive blasting.
This project was completed successfully in 2021, with several notable responses to the engineering challenges.
For the retaining wall, Riley’s solution was a precast concrete gravity wall with rock ground anchors.
We designed the pond uniquely as a large moat with a central bowling green island. We employed an engineered impermeable liner (HDPE) due to the highly porous fracture rock subgrade. Stormwater overflow was directed to a series of specifically engineered, interconnected rockbore soakage devices.
Engineering solutions for building foundations included a mix of piles, mass concrete pads, undercutting and preload.
The wastewater upgrade required extending the public system through neighbouring commercial properties. Riley successfully managed negotiations with landowners, Watercare approvals, design and construction monitoring and compliance.